Resistance heating

ABSTRACT

The invention relates to a tool for a packing machine which contains a heating element in the form of a first moulded body, preferably in the form of a plate which includes at least one conductive connecting element having a certain length. The invention also relates to a method for heating the inventive tools or sheets in a deep forming or sealing unit of the packing machine.

The present invention relates to a tool in a packaging machine, whichcomprises as heating element a first shaped article, preferably a plate,with at least one electrically conductive track of any desired length.The present invention further relates to a method of heating the toolsor the film in a thermoforming or sealing station of a packagingmachine.

These days, foodstuffs are increasingly offered for sale in plasticspackaging. Such plastics packaging consists as a rule of a packagingtray, thermoformed from a plastics film web, and a lid, which is sealedonto the packaging tray after the latter has been filled with theproduct to be packaged, for example foodstuffs.

Prior to thermoforming and during sealing, the packaging film has to beheated. This heating is currently performed predominantly with heatingcartridges, which are for example inserted, preferably pressed, intobores in the sealing tool and thus heat said tool. These heatingcartridges have the disadvantages, however, that the bores have to beproduced very precisely, that the input of thermal energy takes placeslocally, which leads to an uneven, as a rule undesirable, temperaturedistribution in the part to be heated, that failure of a heatingcartridge often goes unnoticed and that removal of the heatingcartridges is virtually impossible. Moreover, the heating cartridgesexhibit a high heat capacity, such that the heating cartridges continueto heat for a long time even after they have been switched off andtemperature peaks of up to 800° C. occur locally in the heatingcartridge.

The object is therefore to provide a tool in a packaging machine whichdoes not exhibit the disadvantages of the prior art and which thereforeexhibits a temperature distribution which is as precisely adjustable aspossible and optionally very homogeneous as well as having rapidresponse behaviour and therefore a short post-heating time, failure of aheating circuit being detectable and the tool being at the same timecheap and easy to assemble and disassemble.

The object is achieved according to the invention with a tool whichcomprises as its heating element a first shaped article, preferably aplate, with at least one electrically conductive track of any desiredlength, wherein the first shaped article is arranged, preferablyclamped, between a second shaped article and a third shaped article,which are both preferably plates, wherein the second shaped article is aworking tool, in particular a sealing frame, a thermoforming mould or aheating plate and wherein the material, the geometry and/or thearrangement of the electrically conductive track is so selected that anydesired temperature distribution may be achieved in the second shapedarticle.

According to the invention, the first shaped article comprises anelectrically conductive track, which is preferably applied to,particularly preferably printed or etched on, the surface thereof orwhich is likewise preferably embedded in, for example laminated into,the first shaped article. The person skilled in the art will understandthat the track may be applied onto or into the first shaped article inany desired manner which permanently ensures the desired arrangement ofthe track.

According to the invention, the track exhibits any desired length,wherein the material of the track is preferably copper, stainless steeland/or aluminium.

The first shaped article exhibits any desired shape or size and is ofany desired thickness. For example, it may be a sheet, film or coatingwith a thickness in the range from preferably 0.1-3000 μm, which isdeposited on or applied to another shaped article, for example, and onor in which the track is arranged.

The cross section of the track preferably varies in accordance with thedesired temperature profile, wherein a small cross section results in arelatively high temperature and a large cross section in a relativelylow temperature. According to the invention, the track is arranged on orin the first shaped article in any desired pattern, wherein it neverintersects itself, however. This pattern is preferably so selected thatthe track is distributed as uniformly as possible on or in the shapedarticle, so making it possible to achieve a very homogeneous temperaturedistribution. It is likewise preferable for the pattern to be soarranged that areas of the shaped article exhibit a higher track densitythan others, whereby the temperature in the areas of greater density ishigher than in the areas of lower density while cross-section andmaterial remain the same.

Clamping of the heating element between the second and third shapedarticles makes possible easy exchange of the heating element. The personskilled in the art will understand that, any other means of connection,for example adhesion, is also suitable provided it ensures precisepositioning of the heating element in the tool between the second andthird shaped articles. Clamping of the heating element advantageouslyoffers the possibility of disassembly, however, for example so that aheating element may likewise be exchanged when a tool is being changed.

The electrically conductive track and the object to be heated arepreferably in as direct contact with one another as possible. It istherefore advantageous for the first shaped article to be arrangedbetween the second shaped article and the third shaped article. Saidarrangement and clamping result in a small distance between the firstshaped article and the second shaped article small. In a further,likewise preferred embodiment, the first shaped article and the secondshaped article are connected irreversibly together, wherein the secondshaped article is a working tool, for example a sealing frame or aheating plate. This means that the distance between the working tool tobe heated and the heat conductor is minimal. The first shaped articleand therefore likewise the electrically conductive track are thenpreferably conformed in shape to the second shaped article, i.e. thethermoforming mould or sealing tool.

In a particularly preferred embodiment, the first shaped article is aplate, however, so making it easy to produce.

It is also preferable for the first shaped article to comprise aplurality of electrically conductive tracks, which are arranged next toand/or above one another and are supplied jointly or separately withvoltage.

The electrically conductive tracks may be arranged nested in oneanother, such that a plurality of tracks determine the temperaturedistribution of one area, or the electrically conductive tracks may berestricted to areas, such that the constitution and wiring of one trackdetermines the temperature distribution solely of one area. Thesearrangements may also be combined with one another.

With the same material, geometry and arrangement, an increase in thevoltage leads to an increased heating power and therefore to highertemperatures, such that the number of possible temperature distributionsis increased considerably, in particular if each individual track issupplied separately with voltage.

The width of the track preferably amounts to between 0.3 and 30 mm,particularly preferably between 0.4 and 3 mm and very particularlypreferably 0.45 and 2 mm. The height of the tracks preferably amounts to0.09-3 mm, particularly preferably 0.3-0.7 mm. Both the width of a trackand its height may vary along the track, whereby the temperatureadvantageously varies along the track. For example, the temperaturealong the track may vary due to a change in the cross-section of thetrack in the area of the seal seam, in such a way that the seal seam isseparable in a desired area while it is not separable in another desiredarea. The temperature in the area of smaller cross-section is higher atthe same voltage and with the same material, and the seam produced isnot separable, than in the area of larger cross section, in which theseam produced is separable.

The present invention further provides a tool which comprises as itsheating element a first shaped article, preferably a plate, with atleast one electrically conductive track of any desired length, whereinthe first shaped article is arranged, preferably clamped, between asecond shaped article and a third shaped article, which are bothpreferably plates, wherein the second shaped article is a working tool,in particular a sealing frame, a thermoforming mould or a heating plateand wherein the electrically conductive tracks, which are arranged nextto and/or above one another, are supplied with voltage separately fromone another in such a way that any desired temperature distribution maybe achieved in the second shaped article.

In the case of separate voltage supply, for example due to each trackhaving its own heating transformer, the heating power of each individualtrack is substantially proportional to the voltage applied, such that adifferent voltage applied to a track leads to a different temperaturedistribution. In this way, the tool may be adapted very simply, withoutresetting, to modified tool or packaging characteristics.

Each of the electrically conductive tracks is preferably individuallycontrollable. In this way, the temperature distribution may be varied inmany different ways, even during the course of the process. For example,each track may have its own controllable voltage supply. Since thematerial and cross-section of a track does not change during the courseof a process, the temperature output is increased if the voltage israised. In addition, the temperature distribution may be varied byswitching individual tracks on or off. Failure of each individual trackis electronically measurable.

In a preferred embodiment, the tool comprises one or more temperaturesensors. In this way, temperature distribution may be measured andspecifically controlled during the process. In this way, it isadvantageously possible to safeguard against excessive temperatures. Thetemperature sensors are preferably incorporated into the first shapedarticle.

The statements made below apply to both subject matters of theinvention.

The distance between the turns of the electrically conductive track orbetween two electrically conductive tracks is preferably <6 mm,particularly preferably <4 mm, so allowing a very homogeneoustemperature distribution.

In a particularly preferred embodiment, the heating element is a printedcircuit board. The board consists of an electrically nonconductivematerial, to which one or more tracks have been applied, which arecapable of individual electrical activation. The material of the trackis preferably copper or aluminium, the thickness of the printed circuitboard amounts preferably to 0.5 mm to 1 mm and the track heightpreferably amounts to 0.09-0.5 mm. The small track height makes itpossible to achieve good thermal homogeneity over the entire heatedsurface area, the risk of overheating being slight. The track may beapplied to the printed circuit board in a manner known to the personskilled in the art, thus for example by printing or etching. The heatingelement is very good value and readily exchangeable and has a longservice life. The printed circuit board may also be of multilayerconstruction, such that a plurality of tracks are arranged one above theother and may be switched on or off and controlled optionallyindependently of one another.

In a further preferred embodiment, the heating element is a heatingfilm. This embodiment also exhibits a particularly long service life anda low weight. The tracks of heating films are likewise thin and flat,such that good thermal homogeneity may also be achieved with heatingfilms and the risk of overheating is likewise low. In addition, theresponse behaviour and thus the post-heating time of a heating elementof this embodiment is particularly short, since heating films exhibit alow intrinsic mass and therefore their heat capacity and/or their heattransmission resistance is low.

The person skilled in the art will understand that the first shapedarticle is either made from a material with a high electricalresistance, for example from ceramic material or a heat-resistant film,or the electrically conductive track is covered in an insulatingmaterial, for example a plastics or a ceramic paper, or that the firstshaped article is coated with a material with a high electricalresistance.

An electrically insulating layer is preferably arranged between thefirst shaped article and the second shaped article, such thatshort-circuiting between parts of the track and the second shapedarticle is reliably prevented.

The insulating material is preferably hard anodised aluminium with alayer thickness of <100 μm, particularly preferably <50 μm. Veryparticularly preferably, the insulating material is applied to thesecond shaped article.

The third shaped article preferably comprises heat insulation orconsists of a heat-insulating material, such that the heat isadvantageously emitted towards the second shaped article, i.e. to thefilm or packaging being processed.

In a preferred embodiment, a resilient layer is additionally arrangedbetween the third shaped article and the first shaped article, saidlayer consisting for example of glass fabric or silicone rubber, or thethird shaped article consists of a resilient material. The first shapedarticle may be so braced together with the second and the third shapedarticle by the resilient layer that contact between the first shapedarticle and the other two shaped articles is ensured throughout. Inparticular, therefore, no air is trapped between the first shapedarticle and the second shaped article, such that the heating power ofthe first shaped article is ideally emitted to the second shapedarticle.

The second shaped article preferably consists substantially of aluminiumor an aluminium alloy, since it has good thermal conductivity in thisembodiment. In a likewise preferred embodiment, the second shapedarticle also comprises a plurality of materials of different thermalconductivities, in order further to assist in the desired temperaturedistribution.

The tool is preferably designed for low voltage, such that the VDEguidelines for protective low voltages are met. The operating voltageparticularly preferably amounts to <80 V, very particularly preferablyto <60 and most preferably to <45 V. The tool is therefore a low-costtool.

The heating element is preferably connected to the tool by means ofelectrical connection components, for example by plug-in connections orby means of terminals. However, a non-detachable connection, effectedfor example by soldering, is also feasible. A detachable connection, forexample of the plug-in or terminal type, is preferred, however, becauseassembly or disassembly and exchange of the heating element are therebymade simple and quick. The connecting lines may be also be produced onthe heating element by (pre)fabrication, so simplifying manufacture andassembly or disassembly of the tool still further.

In a preferred embodiment, the tool comprises at least one first shapedarticle and a plurality of second shaped articles. In this way, aplurality of different packages in any desired formats may thereby beprocessed simultaneously, wherein the temperature distribution for eachof the packages may be different and may also be capable of variation indifferent ways during the course of the process as a result of separatecontrol of each individual track. Even where the tool is provided withjust one track, variable temperature distribution may be achieved byusing different materials, changes in cross-section and variablearrangement of the track over each individual package. Variation of thetemperature distribution during the course of the process is alsopossible, by controlling the supply voltage for example.

In a preferred embodiment, the tool comprises at least one track persecond shaped article. In this way, the temperature distribution may beindividually adjusted for each package and may be different for eachpackage. Failure of a track may be directly identified. Providing everysecond shaped article with at least one temperature probe makes itpossible specifically to control the temperature distribution for eachpackage.

A possible embodiment is also provided by arranging a plurality of firstshaped articles in the tool. The first and second shaped articlesoptionally correspond to one another. However, it is preferable, forexample in the case of a change of format or of packaging size, only toreplace the second shaped article(s) and to adapt the first shapedarticle(s) by reprogramming the control system.

The person skilled in the art will recognise that the tool according tothe invention may be used at any desired location in the packagingmachine. However, it is preferably part of a thermoforming or sealingstation or a film preheating zone.

The tool according to the invention has the advantage of being verysimple and cheap to produce. The temperature distribution may beadjusted in many different ways by the arrangement of the track(s) onand/or in the first shaped article, by the material and/or cross sectionof the track(s) and control of the electrical voltage. The tool issimple to assemble and may be simple exchanged. The failure of one ormore tracks may be detected very quickly and simply. Response behaviouris quick and therefore the post-heating time of the tool is short. It isparticularly suitable for heating the tools or film in a thermoformingor sealing station of a packaging machine.

The present invention therefore further provides a method of heating thetools or the film in a thermoforming or sealing station of a packagingmachine using the tool according to the invention, in which anelectrical voltage is applied to the track of the first shaped article.The temperature distribution in the tool is thus very variable and maybe very precisely adjusted.

In the case of sealing, for example, the track may be arranged with ahigh turn density in the area of the seal seam, such that thetemperature in the area of the seal seam is very high while according tothe invention the package contents are not exposed to any elevatedtemperature. Or the material, geometry and/or arrangement of the trackin a thermoforming machine may for example be such that the areas inwhich the packaging film is more severely stretched are heated to agreater extent than the areas in which the packaging film is notstretched or is stretched only slightly. By changing the supply voltageto the tracks, the temperature distribution may be further adapted, evenduring the course of the process.

The voltage preferably amounts to <70 V. A tool design for low voltagesis therefore sufficient, which saves on cost.

The heating power is preferably controlled with an impulse weldingcontroller by measuring the heat conductor resistance and/or with atemperature sensor. The temperature distribution of the tool may therebybe varied specifically even during the course of the process.

The method is simple and cheap to perform and allows, where necessary,very precisely adjustable temperature distribution and variation evenduring the course of the process.

The present invention further provides a method of resetting a tool fora packaging machine, in which control of the temperature distribution ofthe heat conductor of the tool is reprogrammed and then the secondshaped article(s) of the tool is/are optionally exchanged. This methodis simple and cheap to perform and allows very quick adaptation of apackaging machine, for example in the case of changes of format orchanges to the packages.

The invention is explained below with reference to FIGS. 1-4. Theseexplanations are given merely by way of example and do not restrict thegeneral concept of the invention.

FIG. 1 shows a packaging machine

FIG. 2 shows an embodiment of the tool according to the invention

FIG. 3 is a perspective view of a further tool according to theinvention

FIG. 4 shows an embodiment of the tool according to the invention forthe simultaneous production of 16 packages.

In FIG. 1 a top web 40 is reeled off a supply reel 41 and guided overdeflection pulleys 42 to the individual working stations. The top web 40is conveyed along over a chain conveyor 43, which conveys the top web 40in the direction of arrow 44. A bottom web 45 is conveyed from a supplyreel 46 by a chain conveyor 48 driven via the chain wheels 47 in thedirection of arrow 49. The bottom web 45 is guided over a table 50comprising a cooling plate and an insertion template. The packagecontents 51 are then laid on the moving bottom web 45 and conveyed withit in the conveying direction 49 to the further working stations. Bottomweb 45 and top web 40 are brought together after placing of the packagecontents 51 on the bottom web 45, once the top web 40 has passed througha preheating station 52. The webs 40, 45 lying on one another passtogether with the package contents 51 through the vacuum chamber 53,which consists of a stationary bottom part and a lowerable top part.When the package contents 51 and the webs 40, 45 pass into the vacuumchamber 53 and the vacuum chamber 53 is closed, the top web 40 is heldtaut over the package contents 51 in the manner of a tent. After closureof the vacuum chamber 53, the air is sucked out of the stationary bottompart and thus also from around the package contents 51. Afterevacuation, a sealing plate is pressed against a sealing device (notshown) by means of hydraulic or pneumatic apparatus, for example bycompressed air cushions. The sealed vacuum package then leaves thevacuum chamber 53 and is conveyed over a cooling plate to the cuttingmeans 54.

FIG. 2 shows a tool according to the invention, in the present case aheating plate, such as is used for example in the thermoforming station(not shown in FIG. 1), the preheating zone 52 and/or the sealing zone.The tool, in the present case a heating plate, comprises a first shapedarticle 1, a plastics plate with elevated electrical resistance. Locatedon the plastics plate is a track 2, which is distributed as evenly aspossible over the entire plastics plate. The track 2 has a width of 2mm. The distance 4 between the individual turns of the track 2 amountsin each case to 4 mm, whereby the temperature distribution of the toolis highly homogeneous. The track 2 comprises an electrical connection9,10 at each of its ends, with which it is connected to a voltage source(not shown). The connection to the electrical voltage source issymbolised by the pressure contact 11. The plastics plate 1 is clampedbetween a second shaped article 5, in this case an aluminium plate, anda third shaped article 6, in this case a heat-insulating plate, whereina resilient layer of silicone rubber 8 is additionally arranged betweenthe plastics plate 1 and the heat-insulating plate 6. The person skilledin the art will recognise that the shaped articles 1, 5 and 6 do nothave to be plate-shaped and that the second shaped article 5 may forexample also be a thermoforming or sealing mould. The aluminium plates 5and the heat-insulating plate 6 are screwed together with the screws 13in such a way that the plastics plate 1 is clamped therebetween. A 50 μmthick electrically insulating layer 7 of hard anodised aluminium is alsoarranged between the track 2 and the aluminium plate 5 in order toprevent short-circuiting of the track 2 through the aluminium plate 5.The thickness of the aluminium plate 5 is 10 mm. In operation, thetemperature differences at the underside 12 of the aluminium plate 5 areless than 1° C. even under full load.

The shaped articles 1, 5 and 6 and the layers 7, 8 may comprise holes,so that a reduced pressure may be applied. This embodiment of the toolaccording to the invention is of particular interest when the secondshaped article 5 is not an aluminium plate but rather a thermoformingmould.

The temperature is controlled either via an impulse welding controllerby measuring the heat conductor resistance and/or with a temperaturesensor (for example a PT 100) and a thermostat from M. K. Juchheim,Moltkestraβe 13-31, D-36039 Fulda or Sika Struthweg 7-9, D-34260Kaufungen.

The operating voltage of the heating element is approx. 60 V, withearthed centre on a transformer, such that only approx. 30 V arises asthe highest voltage between the track 2 and the aluminium plate 1. Thetransformer is connected via a transformer switching relay TSRLF made byFSM Elektronik GmbH, Kirchzarten, Germany. The switching relay is thesubject matter of European Patent EP 0 575 715 B1, which is introducedherein by way of reference and thus constitutes part of the disclosure.

FIG. 3 shows a perspective view of a further tool according to theinvention. The heating element comprises a plurality of first shapedarticles 1, in this case printed circuit boards, which comprise at leastone track, a plurality of second shaped articles 5, in this case mouldsfor sealing packaging, and a third shaped article 6, which is aheat-insulating resilient layer, and is clamped to the rear wall 14 bymeans of screws. In order to ensure uniform clamping of the printedcircuit board 1 between the heat-insulating resilient layer 6 and themoulds for sealing 5, the screws are passed through a spacer sleeve 13and screwed into the rear wall 14. The spacer sleeve 13 ensures that thedistance between the rear wall 14 and the moulds for sealing 5 issubstantially the same throughout and therefore the printed circuitboard 1 is pressed uniformly against the moulds for sealing 5. Betweenthe printed circuit board 1 and the moulds for sealing packaging 5 thereis located an electrically insulating layer 7, which ensures that noshort-circuiting occurs between the tracks of the printed circuit board1 and the moulds for sealing 5. Electrical connection is effected bymeans of terminals and/or plugging the cabling into the plug connector 9provided therefor, which is firmly connected to the printed circuitboard 1, for example by means of a soldered joint. Since each mould forsealing packaging 5 comprises a corresponding printed circuit board 1and its own electrical connection 9 for voltage supply and control andat least one temperature sensor (not visible here), the temperaturedistribution of each mould for sealing packaging 5 may be individuallyand specifically controlled. In addition, failure of a track is recordedsimply and directly.

FIG. 4 shows an embodiment of the tool according to the invention forsimultaneous production of 12 packages, in this case for example forpreheating the packages. Here too, the tool comprises the first shapedarticle 1, in this case a heating film, the second shaped articles 5, inthis case aluminium plates, and the third shaped article 6, which is aheat-insulating layer, wherein the heating film 1 is located between thealuminium plates 5 and the heat-insulating layer 6 and is bracedtogether with a rear wall 14. The heating film 1 comprises a largenumber of electrically conductive tracks (not visible here), which maybe supplied with voltage together or separately. In addition, aplurality of temperature sensors are incorporated into the tool,preferably at least one per package. In this way, the temperaturedistribution of each aluminium plate 5 is in itself specificallycontrollable and this tool simultaneously applies different temperaturesto packages.

LIST OF REFERENCE NUMERALS

-   1 First shaped article-   2 Electrically conductive track-   3 Width of track-   4 Distance between the turns of the track/between two tracks-   5 Second shaped article, for example aluminium plate, thermoforming    or sealing mould-   6 Third shaped article, for example heat-insulating plate-   7 Electrically insulating layer, for example silicone rubber-   8 Resilient layer-   9 Electrical connection-   10 Electrical connection-   11 Connection to the electrical voltage source, pressure contact-   12 Underside of aluminium plate-   13 Screws, spacer sleeve for screws-   14 Rear wall-   40 Top web-   41 Supply reel for top web-   42 Deflection pulleys-   43 Chain conveyor, top web-   44 Conveying direction of top web-   45 Bottom web-   46 Supply reel for bottom web-   47 Chain wheels-   48 Chain conveyor, bottom web-   49 Conveying direction of bottom web, conveying direction-   50 Table with cooling plate and insertion template-   51 Package contents-   52 Preheating station-   53 Vacuum chamber-   54 Cutting means

1-20. (canceled)
 21. A tool in a packaging machine, which comprises asits heating element a first shaped article (1), preferably a plate, witha plurality of electrically conductive tracks (2) of any desired length,the first shaped article (1) being arranged, preferably clamped, betweena second shaped article (5) and a third shaped article (6), which areboth preferably plates, the second shaped article (5) being a workingtool, in particular a sealing frame, a thermoforming mould or a heatingplate, characterised in that the electrically conductive tracks (2),which are arranged next to and/or above one another, are supplied withvoltage separately from one another in such a way that any desiredtemperature distribution may be achieved in the second shaped article(5).
 22. A tool according to claim 1, characterised in that thematerial, geometry and/or arrangement of the electrically conductivetrack (2) is so selected that any desired temperature distribution maybe achieved in the second shaped article (5).
 23. A tool according toclaim 21, characterised in that the width (3) of the track (2) amountsto 0.3-30 mm, preferably 0.4-3 mm, particularly preferably 0.45-2 mm.24. A tool according to claim 21, characterised in that each of theelectrically conductive tracks (2) is individually controllable
 25. Atool according to claim 21, characterised in that it comprises one ormore temperature sensors.
 26. A tool according to claim 21,characterised in that the distance (4) between two tracks amounts to <6mm, preferably <4 mm.
 27. A tool according to claim 21, characterised inthat the heating element is a printed circuit board.
 28. A toolaccording to claim 21, characterised in that the heating element is aheating film.
 29. A tool according to claim 21, characterised in that anelectrically insulating layer (7) is arranged between the first shapedarticle (1) and the second shaped article (5).
 30. A tool according toclaim 21, characterised in that the third shaped article (6) comprisesheat insulation or consists of a heat-insulating material.
 31. A toolaccording to claim 21, characterised in that a resilient layer (8) isarranged between the first shaped article (1) and the third shapedarticle (6) or in that the third shaped article (6) consists of aresilient material.
 32. A tool according to claim 21, characterised inthat the second shaped article (5) consists substantially of aluminiumor an aluminium alloy.
 33. A tool according to claim 21, characterisedin that it comprises at least one first shaped article (1) and aplurality of second shaped articles (5).
 34. A tool according to claim33, characterised in that it comprises at least one track (2) per secondshaped article (5).
 35. A tool according to claim 21, characterised inthat it is part of a preheating, thermoforming or sealing station.
 36. Amethod of heating the tools or the film in a thermoforming or sealingstation of a packaging machine with a tool according to any one of thepreceding claims, characterised in that an electrical voltage is appliedto the track(s) (2) of the first shaped article (1).
 37. A methodaccording to claim 16, characterised in that the voltage amounts to <70V.
 38. A method according to claim 16, characterised in that the heatingpower is controlled with an impulse welding controller by measuring heatconductor resistance and/or with a temperature sensor.
 39. A method ofresetting a tool according to claim 21, characterised in that control ofthe temperature distribution, of the heat conductor of the tool isreprogrammed and in that optionally the second shaped article(s) (5) ofthe tool is/are exchanged.